Wirewound variable resistance control and method of making the same

ABSTRACT

Variable resistance control having wirewound resistance element with shorted end turns. A piece of metal secured to each end portion of an electrically nonconductive tape with a bonding material shorts several adjacent turns at each extremity of the resistance element.

United States "Patent, 11 1 1 Miller I 1451 July 31,1973

[75] Inventor:

[ WIREWOUND VARIABLE RESISTANCE CONTROL AND METHOD OF MAKING THE SAME Jack L. Miller, Elkhart, Ind.

73 Assignee: CTS Corporation, Elkhart, Ind.- 22 Filed: June 26,1972 21 Appl. No.; 265,965

[52] US. Cl 338/174, 338/139, 338/160, 29/618 [51] Int. Cl IIOIc 5/02 [58] Field of Search 338/118, 139, 160, 338/162,174,l76,183, 301; 29/610, 618

[56] References Cited UNITED STATES PATENTS Bender et 338/118 2,724,759 11/1955 Daniels ..s3s/174x Primary Examiner-Bemard A. Gilheany Assistant Examiner-D. A. Tone Attorney-John J. Gaydos [57] ABSTRACT Variable resistance control having wirewound resistance element with shorted end turns. A piece of metal secured to each end portion of an electrically nonconductive tape with a bonding material shorts several adjacent turns at each extremity of the resistance element. i 1

12 Claims, 7 Drawing Figures" WIREWOUND VARIABLE RESISTANCE CONTROL AND METHOD OF MAKING THE SAME The present invention. relates toelectrical controls, and, more particularly, to'a wirewound variable resistance electrical control of the type commonly referred to as a fader control and to a method of making the same.

Variable resistance fader controls are commonly employed for alternately changing the volume of a pair of loudspeakers. For example, in an automobile provided with front and rear loudspeakers, itis'p referable to adjust or balance the volume of both of the loudspeakers with a single control.

Many types of fader controls are available on the market. In one particular type of fader control, the end turns of the resistance element are coated with a conturns together with solder have been unsuccessful since the resistnce wire, e.g., Nichrome wire, forming the end turns generally contains chromium which is not readily wettable by solder. Another method of making a fader control, as shown in Bender et a]. U.S. Pat. No. 3,409,855, and assigned to the same assignee as the present invention, utilizes a continuous metal foil disposed between the turns of resistance wire and the insulating core. After attaching terminals" to the 'wirewound resistance element, the metal foil is severed at two places betweenthe end terminals, and the center portion of the metal foil is removed. The remaining end portions of the metal foil preferably are wetted with solder, depending on the application. Although such fader controls are satisfactory, the cost per salable control remains high since the foil cuttingoperation invariably produces some elements having severed or damaged turns which can later break creating a field failure and, therefore, must be scrapped. Also, removal of the ing an elongated strip of metalto the insulating tape, removing pieces .of metal bonded to the tape to produce a laminated ribbon with precisely spaced pieces of metal, and winding a resistance wire around the ribbon. Further objects and advantages of the present invention will become apparent asthe following description proceeds, and the features of novelty'characterizing the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

I is wiped across the step. Attempts to short the end center portion of the foil is a slow and tedious manual I operation resulting in damage to some elements. It would, therefore, be desirable to provide an improved fader control employing a laminated ribboncontaining prespaced pieces of metal bonded to anrinsulating tape for shorting the endturns of a resistance element and to an improved method of making a resistance element for a fader control having shorted adjacent end turns.

Accordingly, it is an object of the present invention to provide an improved fader control. Another object of the present invention is to provide an improved method for shorting adjacent end turns of a resistance element employed in a fader control. A further object of the present invention is to provide an electrical control with a wirewound resistance element having a portion of the turns of wireelectrically connected to prespaced pieces of metal. Still another object of the pres ent invention is to provide a method of shorting end turns of a resistance element by coating an insulating tape with a bonding material having a lower softening temperature than the insulatingtape, thermally bond- Specifically, the present invention is concerned with an improved wirewound resistance element for avariable resistance fader control having precisely prespaced pieces of conductive metal bonded to an electrically nonconductive tape for shorting the end turns of the resistance element. In apreferred embodiment a clad exterior conductive layer is deposited on the metal to protect the metal from undesirable oxidation effects. The present invention is also concerned with an improved method of making the wirewound resistance element by bonding precisely spaced pieces of metal to an electrically nonconductive tape to produce a laminated ribbon. A resistance wire is then wound around the laminated ribbon. The laminated ribbon comprising the spaced pieces of metal and tape can also be combined with an insulating core and the resistance wire is then wound around the laminated ribbon and the core to produce a wirewound resistance element. Pairs of terminals are located at the midpoints of the pieces of metal and are secured to theresistance winding thereby effecting an electrical connection between the piece of metal, the resistance wire,and the terminals. The elements are then .cut to an appropriate length. "If the ele ment is mounted in a cylindrical housing, 'the'element preferably is formed to the shape of the housing to facilitate assembly. a

. For a better understanding of the present invention,

reference may be had to the accompanying drawings wherein the same reference numeralshave been applied to like parts and wherein:

FIG. 1 is an isometric viewvof an electrical control made in accord with the present invention;

FIG. 2 is an exploded view of the control shown in FIG. 1; v i

FIG. 3 shows the relationship between an insulating core,a laminated ribbon, and a resistance wire during the winding operation;

FIG. 4 is a side view of a wound resistance strip shown in FIG. 2 with unsevered pairs of terminals secured to the strip;

FIG. 5 is a top plan view of the resistance element of FIG. 4 after' the terminalcutting and forming opera-.

tion; a

FIG. 6is a grossly enlarged fragmentary section 0 the resistance element takenalong line VI-VI of FIG. 4; and v t FIG. 7 is a diagrammatical representation of the inof the outer end walls of the control and the end wall 11a of the housing 11 forms the other outer. end wall thereof. The open end 11b of the housing 11 is provided with a cutaway section 11c and an arcuate boss 12b extending radially outwardly from the insert 12 fits into the cutaway section 1 1c of the housing 11 to orient the insert 12 with the housing 11. A skirt 120 depending from the end wall 12a and mounted within the housing 1 1 insulates the resistance element 20 from the metal housing 11. A plurality of tabs 13 integral with the housing 1.1 are folded over the end wall 12a of V the insert 12 to secure the housing to the insert. Both of the end walls 11a and 12a of the housing 11 and the insert 12 respectively are provided with apertures 14 and 15 and the rotor 30 is journaled therein.

The resistance element circumposes the rotor 30 and abuts against the inner wall of the depending skirt 120 of the insert 12. More particularly, the resistance element 20 comprises a core 21 of insulating material and a laminated ribbon containing pieces of metal 25a bonded to a tape 25b of insulating material (see FIG. 3) having a plurality of turns of resistance wire 22 wound thereon. When the tape 25b is of sufficient thickness, the resistance wire can be wound directlyzon the laminated ribbon without use of the core 21. The pieces of metal 25a preferably are pieces of metal foil, e.g., copper, having a nickel plate on one side and of a width substantially the same as the tape. Any type of wire, e.g., Nichrome wire, having the proper resistance per unit length can be used. SUitable end terminals 24a and 24b are clinched to the insulating core 21 and the resistance wire 22 thereby effecting an electrical contact with the resistance wire 22 and the metal foil 25a of the laminated ribbon 25. The resistance element 20 is disposed in the insert 12 with the upper edge of the resistance element 20 abutting against the end wall 120. A washer 16 made of an appropriate insulating material is disposed in the housing 11 and abuts against the end wall 11a to provide an insulating barrier between the lower edge of the resistance element 20 and the end wall 11a of the housing 11. The end terminals 24a and 24b project upwardly through slots 12d and l2e provided in the insert 12 and the end portions are formed radially outwardly beyond the slots (see FIG. 1). The end portions of the terminals are partially supported by the walls defining the lower side-of the slots. A collector ring 26 having an opening 26a abuts against the end wall 12a of the insert 12 and a center terminal 27 extends radially outwardly from the collector ring 26 through a slot 12f provided in'the insert 12. The rotor 30 molded of a suitable insulating material is provided with a cylindrical shoulder 30a engaging the inner edge of the opening 26a for positioning the collector ring coaxially with the apertures 14 and 15.

For the purpose of transferring electric current from theresistance element'20 to'- the collector ring 26, acontactor 31 having a pair of spaced contact fingers 32a and 32b electrically connected to each other wipingly engages the resistance element 20. The contactor 31 comprises a ring portion 31a in slideable engagement with the collector ring 26, and a pair of downwardly extending cars 33 integral with the ring portion 31a and received in a pair of diametrically disposed grooves 3012 provided in the rotor constrain the contactor 31 to rotate with the rotor 30. In order to limit rotation of the contactor 31, the rotor is provided with an arcuate boss 34 engageable with a stop 11d (see FIG.

2) extending inwardly from the end wall 11a of the housing 11. A hollow'shaft 35, of appropriate design, fixedly secured to the rotor 30 extends outwardly of the housing.

Referring now particularly to a preferred method of making the resistance element 20, precisely cut pieces of metal foil 25a are bonded to a suitable elongated insulating tape 25b, e.g., a polyester tape. Preferably the insulating tape is coated with a bonding material, e.g., a polyethylene coating, having a lower softening temperature than the tape 25b for thermally bonding the pieces of metal foil at spaced intervals to the tape. The bonding material can be readily softened by applying heat to the metal foil and the tape to secure the metal foil to the tape. The tape 25b with the metal foil bonded thereto is commonly referred to as a laminated ribbon 25. Any type of suitable cement can also be employed for securing the metal foil to the insulating tape. In-

stead of precisely locating and securing the individual pieces of metal foil 25b on the insulating tape 25a at spaced intervals, a continuous metal foil can be secured to the insulating tape and precisely spaced portions of metal foil can be readily removed, e.g., by chemical etching. The laminated ribbon 25 with spaced pieces of metal foil is then placed against the core of insulating mateial 21 preferably a flat strip with the tape side of the laminated ribbon 25 flush against a flat side of the core. The insulating core 21 and the ribbon 25 are then fed'into a winding machine and the resistance wire 22 is wound around the insulating core 21 and the ribbon 25. securing the ribbon to the core and producing a wound resistance strip containing spaced pieces of metal foil 25a shorting adjacent turns of resistance wire. When the tape 25b is of sufficient thickness such as to avoid buckling, the resistance wire 22 can be wound directly on the laminated ribbon. At the present time since the insulating core 21 is cheaper than the tape 25b, the laminated ribbon 25 is'preferably combined with the core 21 and wound with the resistance wire 22. At the midpoints of each of the metal foils 25a of the ribbon 25, pairs of terminals 23 (see FIG. 4) are clinched to the wound resistance strip electrically connecting the resistance wire 22 and the metal foil 25a of thevribbon to the terminal pairs 23. The wound resis' tance strip is then cut to short lengths by removing a section 23a from each pair of terminals 23 to produce a resistance element 20 having a pair of end terminals 24a and 24b at the ends thereof. The cutting operation also divides each of the pieces of metal foil 25a of the laminated ribbon 25 into two separate parts 25c and 25d. In specificapplications solder may be applied to i the pieces of metal foil to increase the electrical contact between the wire 22 and the metal foil 25a. In a particular embodiment, a laminated ribbon 25, 0.197 inches wide, comprising pieces of nickelplated l oz. copper foil 1.55 inches in length bonded to a,0.0025 inch thick polyester insulating tape with 0.410 inches between each piece of metal foil, was positioned on an insulating core 0.200 inches wide.

By connecting the end terminals 24a and 24b of the resistance element of the fader control 10 to a pair of not-shown loudspeakers and the center terminal 27 to one side of a not-shown input signal, turning of the shaft 35 of the fader control 10 between one end of rotation to midpoint rotation causes the resistance that the control 10 introduces into the one loudspeaker circuit to decrease, while the resistance introduced into the second loudspeaker circuit remains essentially zero. Therefore, the volume of the first loudspeaker increases from a minimum to a maximum value while the volume of the second loudspeaker remains at maximum. At midpoint rotation,'the resistance introduced. into each loudspeaker circuit is essentially zero and both loudspeakers are at maximum volume. While continuing to turn the shaft 35 in the same direction from midpoint rotation to full rotation, the resistance introduced by the control into the first loudspeaker circuit' remains essentially zero while the resistance introduced into the second loudspeaker circuit increases.

Therefore, over the second half of the rotation of the shaft 35, the volume of the first loudspeaker remains at a maximum while the volume of the second loud- While there has been illustrated and described what is at present considered to be a preferred embodiment of the presentinvention and a method of making the same, it will be appreciated that numerous changes and modifications are likely'to'occur to those skilled in the art, and it is intended in the appended claims to cover all those changes and modifications which fall within the true spirit and scope of the present invention. I

What is claimed as new and desired to be secured by Letters Patent of the United States is: y 1. A variable resistance control comprising a housing, a wirewound resistance element disposed in said housing, said resistance element comprising an insulating tape, a first piece and a second piece of metal spaced from the first piece bonded to the insulating tape, a resistance wire wound around the tape with adjacent turns spaced from each other, the first piece of metal shorting a plurality of the turns of the resistance wire at one end thereof to define a first shorted portion, the second piece of metal shorting a pluralityv of the I and said first and second pieces of metal are thermally bonded to the insulating tape.

, 5. The control of claim 4, wherein the insulating tape is a polyester tape and the bonding material is polyethylene.

6. The control of claim 5, wherein the polyethylene bonding material is a coating on the polyester insulating tape.:

7. A variable resistance control comprising a housing, a wirewound resistance element disposed in said housing, said resistance element comprising an insulating core, an insulating tape in juxtaposition to the insulating core, a first piece and a second piece of metal foil spaced from the first piece bonded to the insulating tape, a resistance wire wound around the core and the tape with adjacent turns spaced from each other, the metal foil having a width substantially equal to the width of the tape, the first piece of metal foil shorting a-plurality of the turns of the resistance wire atone end thereof to define a first shorted portion, the second piece of metal foil shorting a plurality of the turns of the resistance wire at the other end thereof todefine a second shorted portion, said resistance wire'havinga trically connected to said first shorted portion of the turns of the resistance wire at the other end thereof to define a second shorted portion, said resistance wire having a single unshorted portion extending between the first and second shorted portions, a first end tenninal electrically connected to said first shorted portion of the resistance wire, a second endterminal electrically connected to said second shortedportion of the resistance wire, a contactor comprising a pair of spaced fingers wipingly engaging the resistance element between the ends thereof, and a third terminal electrically connected with the contactor. t

2. The control of claim 1, wherein an insulating core is disposed adjacent to the tape and the resistance wire is wound around the tape and the core. I

3. The control o'fclaim I, wherein said first and second pieces of metal comprise copper with a clad exterior surface of nickelengaging the resistance wire.

4. The control of claim 1, wherein a bonding material having a lower softening temperature than the insulating tape is disposed between the metal and the tape,

resistance wire,'a second end terminal electrically connected to said second shorted portion of the resistance wire,a contactor comprising a pair of spaced fingers wipingly engaging the resistance element between the ends thereof, and a third terminal electrically con nected with the contactor.

, 8. A method of shorting a portion of a wirewound re sistance element comprising the steps of bonding pieces of metal to an insulating tape to produce a laminated ribbon, winding a resistance wire around the laminated ribbon with adjacent convolutions of the resistance wire spaced from each other and in electrical contact with said pieces of metal, and securing a plurality of electrically conductive terminals to. the resistance wire. Y

9. The method of claim 8, wherein the step of bonding pieces of metal to an insulating tape comprises the step of coating the insulating tape with a bonding material, securing an elongated strip of metal to the insulating tape wih the bonding material, and removing spaced pieces of metal bonded to the insulating tape to produce a laminated ribbon with precisely spaced pieces of metal. l

10. The method ofv claim 9, wherein the insulating tape is a polyester and the bonding material is a polyethylene.

11. The method of claim 9, wherein the first mentioned spaced pieces of metal are removed by chemical etching. 1 I

12. The method of claim 9', wherein the step of securing an elongated strip of metal to the insulating tape insufficiently soft to effect a bond between the metal and the tape.

t I I i 

1. A variable resistance control comprising a housing, a wirewound resistance element disposed in said housing, said resistance element comprising an insulating tape, a first piece and a second piece of metal spaced from the first piece bonded to the insulating tape, a resistance wire wound around the tape with adjacent turns spaced from each other, the first piece of metal shorting a plurality of the turns of the resistance wire at one end thereof to define a first shorted portion, the second piece of metal shorting a plurality of the turns of the resistance wire at the other end thereof to define a second shorted portion, said resistance wire having a single unshorted portion extending between the first and second shorted portions, a first end terminal electrically connected to said first shorted portion of the resistance wire, a second end terminal electrically connected to said second shorted portion of the resistance wire, a contactor comprising a pair of spaced fingers wipingly engaging the resistance element between the ends thereof, and a third terminal electrically connected with the contactor.
 2. The control of claim 1, wherein an insulating core is disposed adjacent to the tape and the resistance wire is wound around the tape and the core.
 3. The control of claim 1, wherein said first and second pieces of metal comprise copper with a clad exterior surface of nickel engaging the resistance wire.
 4. The control of claim 1, wherein a bonding material having a lower softening temperature than the insulating tape is disposed between the metal and the tape, and said first and second pieces of metal are thermally bonded to the insulating tape.
 5. The control of claim 4, wherein the insulating tape is a polyester tape and the bonding material is polyethylene.
 6. The control of claim 5, wherein the polyethylene bonding material is a coating on the polyester insulating tape.
 7. A variable resistance control comprising a housing, a wirewound resistance element disposed in said housing, said resistance element comprising an insulating core, an insulating tape in juxtaposition to the insulating core, a first piece and a second piece of metal foil spaced from the first piece bonded to the insulating tape, a resistance wire wound around the core and the tape with adjacent turns spaced from each other, the metal foil having a width substantially equal to the width of the tape, the first piece of metal foil shorting a plurality of the turns of the resistance wire at one end thereof to define a first shorted portion, the second piece of metal foil shorting a plurality of the turns of the resistance wire at the other end thereof to define a second shorted portion, said resistance wire having a single unshorted portion extending between the first and second shorted portions, a first end terminal electrically connected to said first shorted portion of the resistance wire, a second end terminal electrically connected to said second shorted portion of the resistance wire, a contactor comprising a pair of spaced fingers wipingly engaging the resistance element between the ends thereof, and a third terminal electrically connected with the contactor.
 8. A method of shorting a portion of a wirewound resistance element comprisinG the steps of bonding pieces of metal to an insulating tape to produce a laminated ribbon, winding a resistance wire around the laminated ribbon with adjacent convolutions of the resistance wire spaced from each other and in electrical contact with said pieces of metal, and securing a plurality of electrically conductive terminals to the resistance wire.
 9. The method of claim 8, wherein the step of bonding pieces of metal to an insulating tape comprises the step of coating the insulating tape with a bonding material, securing an elongated strip of metal to the insulating tape wih the bonding material, and removing spaced pieces of metal bonded to the insulating tape to produce a laminated ribbon with precisely spaced pieces of metal.
 10. The method of claim 9, wherein the insulating tape is a polyester and the bonding material is a polyethylene.
 11. The method of claim 9, wherein the first mentioned spaced pieces of metal are removed by chemical etching.
 12. The method of claim 9, wherein the step of securing an elongated strip of metal to the insulating tape includes the step of heating the bonding material until sufficiently soft to effect a bond between the metal and the tape. 